1. Field of the Invention
The present invention generally relates to the receiver and method of block code transmission, and more particularly to receiver and method that use Feed-Forward Equalizer (FFE) to convert the block signal into a signal with minimum phase, and further use Maximum Likelihood Sequence Estimation (MLSE) to generate the proper signal.
2. Description of the Prior Art
In recent years, continuous requirements for high-speed communication products have become the major object for many projects in IEEE802.11 Committee, one of them is how to use the new standard of 2.4 GHz within the frequency spectrum. Wherein FCC Part 15.247 uses spread spectrum techniques to transmit the packet of data over 10 Mbps. However, IEEE802.11 Committee only involves in the data transmission with the speed between 1 Mbps to 2 Mbps with the technology of Frequency Hopping (FH) or Direct Sequence (DS) Spread Spectrum (SS), while IEEE802.11b has established the transmission standard of Complementary Code Keying (CCK) that transmits data over 11 Mbps. It adopts the original property of Spread Spectrum (SS) to comply with the FCC requirement for Spread Spectrum signaling, with the new technology for receiver and by decreasing the average spectrum density of transmission, it increases the robustness of the signal to against interference. In addition, the new technology for receiver uses the spectral redundancy to eliminate self-interference created by multipath distortion. However, an extra equalizer is needed for 11 Mbps CCK modulation in order to improve the performance.
FIG. 1 is illustrating the structure of a common receiver that meets the requirement of IEEE802.11 CCK. As shown, the receiver 10 receives the block signal transmitted from a transmitter (not shown), and the block signal is further processed by a Channel Matched Filter (CMF) 11 to improve S/N ratio. Next, the block signal will be processed by Feed-Forward Equalizer (FFE) 12, Inter-Symbol Interference (ISI) eliminator 13 and Feedback Equalizer (FBE) 15 to eliminate the inter-symbol interference. Finally, the receiver will identify what the signal is with a slicer 14.
Although the receiver 10 uses the Channel Matched Filter (CMF) 11 to increase the S/N ratio of the block signal, however, the length of channel response is also increased. Moreover, if the original channel response is with minimum phase, after the Channel Matched Filter (CMF) 11, the channel response will become to be with non-minimum phase, which will cause the length of Feedback Equalizer (FBE) 15 to increase, so as the convergence of FBE become worse. Especially, in the wireless environment that the S/N ratio is worse, the Feedback Equalizer (FBE) 15 often converges to wrong settings; so, whatever long packet or short packet will not be received properly.
FIG. 2 is illustrating that the signal has been divided into a plurality of block signals for transmission. As shown in FIG. 2, indicating symbol inserted between block signals will reduce the interference within, the receiver receives the signal properly only by eliminating the interference, which will simplify the design of receiver and increase the receiving capability of the receiver. FIG. 3 is illustrating that, in an indoor wireless communication environment, the channel response is often with minimum phase and there is less pre-cursor interference. That means the symbol signal B will not interfere the signal block 1, the symbol signal C will not interfere the signal block 2, and the symbol signal D will not interfere the signal block 3. Thus, if the receiver is able to eliminate the inter-symbol interference created by the previous signal block interfering to the incoming signal block by adding (or deducting) the received signal block with the signal block being detected, as shown in FIG. 4.
The same idea can apply to the modulation technology for IEEE802.11b Complementary Code Keying (CCK); similar signal transmission is shown in FIG. 4. In FIG. 4, the interference that signal block 1 interfering the signal block 2 can be eliminated first, and then the signal included in the signal block 2 will be resolved properly, so, the symbol signal will be no more transmitted to save bandwidth. In the modulation technology for IEEE802.11b Complementary Code Keying (CCK), each block in FIG. 4 will be regarded as a Symbol, and every Symbol includes 8 Quadrature Phase Shift Keying (QPSK) signal and every QPSK signal can be regarded as a Chip, that is, every Block (or Symbol) includes 8 Chips.